Woodworm
and woodworm treatment

What
is Woodworm

The
most frequent insect pest in wood in buildings in the UK is the common furniture
beetle, Anobium punctatum, better known as woodworm.

It has a 5 year life cycle, maximum. We need to look at wood preservatives and
their performance - wood treatment is always aimed at breaking the egg laying
cycle - so what is that cycle and how does it influence insecticide treatment?

Common
furniture beetle starts life as an egg; these are laid on a suitable timber surfaces
- but some of these surfaces are cracks and crevices, end grain and, very importantly,
down the old emergence holes in pupal chambers and tunnels. The larvae hatch,
bore into the sap wood when they remain causing the damage; the larvae are the
feeding and growing stages and are by far the longest stage of the insect's life
cycle.

At some stage the
larva moves close to the surface and constructs a pupal chamber in which it pupates.
Between May and August the adult emerges from its pupal skin and chews its way
out leaving the familiar 'woodworm holes'. When they cut
their way out they do not feed! When emerged they mate and lay eggs, frequently
rapidly and very often down the old emergence holes in the pupal chambers and
tunnels, i.e.. well below the surface. Indeed, both mating and egg laying can
take place within the emergence hole itself.

Spray
applied preservatives

The
spray applied timber preservative can contain a contact insecticide such as Permethrin
or Cypermethrin. Basically all the insect has to do is to come into contact with
this material - the insect doesn't have to ingest it; if it did it would also
kill it. So one could theoretically argue that contact insecticide has both stomach
and contact action. Using an alternative Insecticide, like a Boron based product,
only kills the 'grub' or lava when it eats wood. It acts as a stomach 'poison'
by affecting the enzymes in the gut. The advantage of this type of treatment is
that it does NOT kill flies or spiders - only wood borers - therefore leaving
them for the Bats. Boron based products are also superior because that have no
vapour - so the active part - the Borate - never leaves the timber, giving permanent
protection.

When the wood
is sprayed with the preservative it penetrates the surface, probably between 2-6
mm, to leave a protective 'envelope' of insecticide. Any stages initially deluged
by the fluid in the 'envelope' will be killed. Those remaining beneath the treatment
will survive and continue activity. Clearly these stages will have to come into
contact with the insecticidal 'envelope' at some stage for it to be effective.
This occurs, at least theoretically, when (a) adults emerge, and (b) larvae hatch
from surface laid eggs.

The
adults: Adults should be killed as they try to cut their way out of the wood when
they cross the 'envelope' containing the contact insecticide; remember they do
not feed and must come into contact with the insecticide to have an effect. Therefore
the contact acting insecticide should not let them through the treated envelope
(non contact insecticides will have no effect on this stage). Indeed, both Permethrin
and Cypermethrin like most pyrethroid derived insecticides, are fast acting. Since
it does take time to cut emergence tunnels clearly one would expect these beetles
to be affected quite rapidly. If under such circumstances, however, they can completely
emerge successfully then they haven't been affected by the treatment: they are
then free to mate and lay eggs.

Egg
larvae

It
is well documented that common furniture beetle mates and lays eggs down old tunnels,
often well below the surface. Rarely, this can cause hatching beneath the applied
treatment, be it a contact insecticide or non contact type insecticide, if the
treatment was inadequately applied (two good coats to refusal). As such this will
lead to successful hatching and larval survival. Hence the infestation continues,
and the treatment must therefore be deemed to have failed.

Books
- guides to insects, rots, moulds and damp

Woodworm
Control - why we use wood preservatives

In
the UK we are mainly concerned with woodworm treatment for Common Furniture Beetle,
(Anobium punctatum, in Latin). We need to practice safe woodworm beetle treatment
because of the long term damage that the woodworm larvae (grubs) cause in structural
and decorative woodwork in domestic houses and commercial buildings.

Knowledge
of the life cycle of the common furniture beetle (usually just called 'Woodworm'
for short) is important when carrying out woodworm treatment because we cannot
stop adult Woodworm beetles emerging using normal timber treatments, no matter
which surface applied woodworm treatment product we use. To eventually cure woodworm
we first need to break the 'egg laying cycle'.

Common
furniture beetle starts life as an egg. These are laid on a bare, unpainted timber
surface, or in cracks and crevices, end grain and down old emergence holes.

These larvae hatch, bore into the sap wood, where they cause most of the damage.
The larvae feed on the wood and this 'worm' becomes larger for up to 5 years.
At some stage the wood worm moves close to the surface and constructs a pupal
chamber.

Between May and
August the adult emerges from its pupal skin and chews its way out leaving the
familiar 'woodworm holes'. When they cut their way out they are not actually feeding
- the adult does not eat! When the adult beetles have emerged they mate and lay
eggs, frequently down the old emergence holes and into the pupal chambers and
tunnels. Sometimes both mating and egg laying can take place within the emergence
hole itself.

How
to stop Woodworm

Woodworm
treatment is essential, if active woodworm is present, in order to prevent
woodworm eggs from successfully boring into the timber and continuing the woodworm
life cycle. If woodworm, or worse still Death Watch Beetle, (or even worse still
House Longhorn Beetle) is allowed to continue to eat your wood, it will be structurally
weakened by the multitude of internal tunnels and beetle flight escape holes.
These exit holes are evidence of an attack of some type of woodworm, but the size
of the exit hole is important in determining the beetle species and hence its
life expectancy. Death watch Beetle has a much longer cycle (8 to 10 years) than
Common Furniture Beetle (3 to 5 years), so woodworm treatment, as a woodworm killer,
has to be adapted to suit the insect involved. Timber treatment is only part of
the woodworm story. Dampness also plays an important part in woodworm attack,
(woodworm prefer damp or wet timber) so timber treatment must take account of
damp, its source and its control or elimination. Fortunately, Boron based products
love moisture - they 'seek' the dampest parts of the wood, thus protecting the
most vulnerable areas.